and on Alcoholic EngineS4 37 



"to 



discharge of heat from a furnace by means of the highly rari- 

 fled ascending gases, seems to render any thing like z-esistance 

 to instantaneous expansion unnecessary and improbable. 



Mr. Haycraft, speaking of combustion, says, " This forma- 

 tion [of carbonic acid] does not consist of a conversion of 

 oxygen into carbonic acid, but of a union of two ingredients 

 into a compound having an absolute capacity for caloric 

 equal to one of the ingredients only ; namely, the oxygen gas : 

 consequently the whole absolute heat of the carbon is rendered 

 free." Now on this it need only be remarked, that Mr. Hay- 

 craft seems to have entirely forgotten that we are still totally 

 in the dark as to the absolute quantity of heat in bodies. In- 

 deed, we do not even know which of two bodies of different 

 compositions contains most heat ; and whilst this is the case, 

 it is no wonder that we are ignorant of their exact propor- 

 tions. Mr. Haycraft has, no doubt, at great trouble and ex- 

 pense rendered an important service to science, by showing in 

 a more satisfactory way than had been done, that, under equal 

 volumes, the specific heats of the gases are equal : but we are 

 not therefore warranted to conclude that their absolute heats 

 are equal. That a knowledge of the specific heats throws little 

 or no light on the absolute quantity, is plain from the cir- 

 cumstance, that steam, though inferior to water in the former 

 quality, much exceeds it in the latter. If such be the case 

 with the same body under different forms, — how much more 

 so of different bodies? 



As steam is one of the most useful mechanical agents, its 

 powers are deserving of minute examination. They have long 

 engaged the attention both of our own countrymen and of 

 foreigners ; and on some of their opinions and experiments I 

 now take the liberty of making a few remarks. 



On opening a pipe connected with a steam-boiler and con- 

 densing a certain weight of the vapour in a vessel of cold 

 water, M. Clement found that the increase in the water's tem- 

 perature was independent of the elasticity of steam in the 

 boiler ; at least it was sensibly so whilst that elasticity was 

 equal, double or triple the atmospheric pressure. From this 

 he inferred, that the entire heat in a given weight of steam in 

 a state of saturation must be the same at all temperatures. 

 But this conclusion, though pretty generally acquiesced in, has 

 been rather too hastily drawn to bear examination. It is well 

 known, that an elastic fluid when allowed to expand without 

 any accession of heat will be reduced in its temperature ; but 

 if at the same time in contact with a hotter body, or one which 

 possesses its former temperature, it will readily absorb heat 

 from that bod}'. When, therefore, the steam which possessed 



double 



